This application claims priority from Japanese Patent Application No. 237656/2000, the disclosure of which is incorporated herein by reference.
This invention relates to a contactless identification system for logistic systems, object management systems, an antenna coil and associated contactless identification device utilized in a contactless identification system.
Conventionally, a logistic system or an objects management system of this kind already exists, e.g. a library management system handling the checkout and return of a book. In such a system, a management tag (data carrier) is fixed with paste or the like on each of the books to be managed by the library, and when a checkout or return process is taken, the book is set on the predetermined position near the antenna of the identification device. Data transmission then takes place between the tag and the antenna of the identification device by such transmission means as disclosed by U.S. Pat. No. 2,683,305, for example. That is to say, a transmission signal, generated by modulation of the set carrier frequency, is sent from the antenna of the identification device to the tag. The tag performs reading/writing, as well as electric power supply receipt, in accordance with the signal transmitted from the identification device antenna. Transmission then takes place by the so-called Load Switching Method in which the required data may be sent out from the tag to the antenna of the identification device by altering the load impedance of the antenna on the tag, in accordance with the read-out data on the tag side.
In this manner, the book checkout and return process is carried out via antenna-tag transmission, once the identification device has obtained the necessary information through the antenna.
However, the following problems exist with this conventional technology.
When a number of books pile up, the distances between the tags fixed on the books and the antenna also increases. When transmission is performed between the fixed antenna and the multiple tags in such arrangement, some tag distances from the antenna are longer than others and thus the transmission distance may be too great. FIG. 9 shows magnetic lines generated by the fixed antenna coil. In such a magnetic field, the magnetic force at each of points A, B, C, D and E, where the multiple tags are positioned at various distances from the antenna coil, are shown by the length of the magnetic vector. (All tags are assumed to be positioned parallel to the antenna coil.) Here, the tag at point A crosses over the maximum magnetic force generated in the antenna coil, and maximum energy is supplied to the tag. The farther a crossing point lies from the antenna coil along the line intersecting the antenna coil at right angles, such as at points B and C, the weaker the magnetic force becomes, and the weaker the energy supplied to the coil. Also, the farther a crossing point lies from the center of the antenna coil along the lines parallel to the antenna coil, such as points D and E, the weaker the component of the magnetic force crossing over the tag becomes, the weaker the energy supplied to the coil. FIG. 10 shows different levels of electric power at different amplitudes, as supplied to a tag at each point. In this manner, some of the multiple tags, positioned at various distances from the fixed antenna, are at an insufficient distance for transmission. For this reason, the conventional technology suffers from not being able to read all tags accurately.
Another problem with the conventional technology is that multiple tags are not be read accurately at once, as mutual interference between the tags fixed on the books lowers the resonance frequency of the tags.
In order to resolve this problem, one known method is to preset tag resonance frequencies to higher frequencies. However, a discrepancy occurs between the tag resonance frequency and the antenna of the identification device, such that the transmission distance deteriorates considerably and results in an insufficient reading of all multiple books in the pile.
This invention resolves the above mentioned problems associated with the conventional technology. The purpose of this invention is to provide a contactless identification system and the antenna coil with a reliable transmission path for multiple tags.
The invention provides a contactless identification system comprising a data carrier for attachment to objects, and an antenna section which communicates with the data carrier, where the antenna section includes an antenna coil with an opening to accommodate the objects.
Also, the system can comprise a guidance means to guide transfer or movement of the antenna coil with respect to the objects set at the predetermined position so that the objects pass through said opening.
The system can also comprise an antenna transfer means to transfer or vary the position of the antenna coil with respect to the objects set at the predetermined position so that the objects pass through the opening.
Another embodiment may comprise an objects transfer means to transfer or move the objects with respect to the antenna coil set at the predetermined position so that the objects pass through the opening.
Also, this invention relates to the data carrier to be attached to the objects and an antenna coil which is utilized for a contactless identification system, in which the identification device possesses an antenna section which communicates with the data carrier, the antenna coil possessing an opening to accommodate objects.
This invention also relates to the contactless identification means for identifying objects by performing transmission between the data carrier attached to the objects and the antenna coil possessing an opening, including a step to perform transmission with said data carrier after relative transfer of said objects and the antenna coil, so that the data carrier attached to the objects passes through the antenna opening.
Also, the step to relative transfer or move the objects and the antenna coil with respect to each other and to perform transmission with the data carrier includes a step to set the objects at a predetermined position and a step to move or transfer the antenna coil position so that each data carrier attached to the objects passes through the opening.
Also, the step to transfer the antenna coil includes a step shaking the antenna coil around a shaft supporting the antenna coil thereon with room allowed for shaking, so that each of the data carriers attached to the objects passes through the opening.
Also, the step to relative transfer the objects and the antenna coil and to perform transmission with the said data carrier, includes a step to transfer the objects against the antenna coil set at a predetermined position so that each data carrier attached to the objects passes the opening.